Please help solve thabks

5. Po Po's Kitchen of restaurants operates a number of restaurants in the Klang Valley. Recently, headquarters received a number of complaints from their Kuala Lumpur branch customers regarding the long waiting time for their food to arrive at their table. The manager looks at a sample of 81 service logs indicating waiting times from the moment the order is made until the order is served to the customer. The sample average waiting time (from order to food on table) is 18 minutes. The standard deviation is 2.1 minutes. According to the customers' complaints, it takes 20 minutes for their food to arrive at their table from the moment they make their order. (a) Construct and interpret a 95 percent confidence interval for the population mean of waiting times in the restaurant. [6 marks] (b) Without further calculations, at 5 percent significance level, can the manager of the Kuala Lumpur branch claim that the customers' complaints are not reasonable? [3 marks] (c). Without further calculations, if the confidence interval changes from 95 percent to 99 percent, what would happen to the interval? [3 marks] (d) Explain why a 95 percent confidence interval can be used in hypothesis testing at 5 percent significance level. [3 marks]3. iii. Explain why a turning point is defined as maximum when the value of second order condition is negative. [2 marks]